Power semiconductor devices, e.g., metal oxide field effect transistors (MOSFETs) such as double diffused metal oxide semiconductor (DMOS) transistors or insulated gate bipolar transistors (IGBTs), can suffer a permanent change in their electrical properties or can be destroyed if exposed to high-energy particle radiation or high-energy photon radiation.
There are three known major mechanisms that can lead to such a deterioration of a power semiconductor device. If ion-induced charges are separated by the electrical field of the reverse voltage, holes accumulate under the gate oxide due to the field geometry. When the breakdown voltage of the gate oxide is surpassed, in particular with negative gate-source voltage, a local breakdown of the gate oxide can result. If the integrity of the gate oxide (GOX) is locally destroyed the gate leakage current can rise and the control effect of the gate may be lost. This phenomenon is called Single Event Gate Rupture (SEGR).
Ion-induced avalanche generation, caused by a heavy ion impact from the radiation which creates a local, very high density electron-hole plasma, can lead to a short, but high current pulse under an applied reverse voltage. The high concentration of charge carriers results in a change of the electrical field with a steepening near the n+-doped drain region of the substrate. If avalanche generation occurs the holes flow back to the source contact and can activate the parasitic bipolar transistor (BIP), leading to a self-sustained, destructive process (second breakdown). Such a local, massive damage to the silicon substrate can lead to a rise of the source-drain leakage current, and even to the complete loss of the drain-source blocking capability. This phenomenon is called Single Event Breakdown (SEB). SEGR and SEB together will be referred to as Single Event Effect (SEE).
A third mechanism is the charging of the gate oxide with positive charge through ionizing radiation. This phenomenon is called Total Ionizing Dose (TID) effect. In contrast to SEB and SEGR effects, TID effects does not lead to the destruction of the device, but to a drift of its electrical parameters, especially the threshold voltage.
There exist some conventional approaches for making a power semiconductor device more resistant to radiation. For example, for radiation-hardening the device against SEB, it has been suggested not to use an n−/n+-backside contact or to lower the source doping; against TID to reduce the thickness of the gate oxide; and against SEGR to increase the thickness of the gate oxide in contradiction to the TID-hardening measure, or to narrow the width of the neck regions between the body regions. The known approaches typically deteriorate electrical parameters of the power semiconductor devices such as the important drain to source resistance in on-state RDS(on), and have partially been suggested for devices which could not reach a low on-state resistance RDS(on).
In view of the above, there is a need for improvement.